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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A technician is troubleshooting a system with low suction pressure, high superheat, and a frosted expansion valve body, but a warm liquid line entering it. What is the most likely cause?

These symptoms (low suction, high superheat, frosted TXV but warm liquid line) strongly indicate a restriction upstream of the TXV, such as a clogged filter dry

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Question: A technician is troubleshooting a system with low suction pressure, high superheat, and a frosted expansion valve body, but a warm liquid line entering it. What is the most likely cause?

Answer options:

  • Overcharge of refrigerant
  • Low condenser airflow ✅ Partially restricted filter dryer or liquid line
  • Compressor internal failure

Correct answer: Partially restricted filter dryer or liquid line

Explanation: These symptoms (low suction, high superheat, frosted TXV but warm liquid line) strongly indicate a restriction upstream of the TXV, such as a clogged filter dryer or a crimped liquid line. This causes a premature pressure drop and flash gas before the valve.

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